SUMMARY The goal of this project is to identify the epigenomic changes in adult stem cells during aging and in response to rejuvenating interventions, with the objective to restore youthful function to old stem cells. The adult brain contains a reservoir of neural stem cells (NSCs) that can give rise to new neurons, astrocytes, and oligodendrocytes throughout life. However, during aging, the ability of NSCs to give rise to new neurons dramatically deteriorates. Exciting emerging data suggest that NSC decline can be reversed in part by blood factors, exercise, and diet, indicating that specific molecular mechanisms could integrate these external stimuli and reverse the decline of these cells. However, the molecular bases of the reversible age-dependent changes in NSCs in response to environmental cues have been elusive. Our lab has embarked on a massive effort to identify changes in the epigenome and transcriptome of NSCs during aging. Our results have uncovered a new chromatin signature ? broad H3K4me3 domains ? that marks genes that are critical for NSC identity. Intriguingly, this signature also marks genes with increased transcriptional levels and consistency (i.e. reduction of transcriptional noise). The central hypothesis of this Project is that chromatin changes during aging reduces the robustness of transcriptional outputs, and that restoring such epigenetic changes could rejuvenate the transcriptional output and function of old NSCs. As such, the Specific Aims of this proposal are: 1. To understand how broad H3K4me3 domains and their transcriptional outputs are influenced by increasing age and by rejuvenating strategies in old animals; 2. To specifically modulate broad H3K4me3 domains at critical functional genes in NSCs to reprogram transcriptional outputs and function in old NSCs; 3. To generate systems-level aging models based on single cell gene expression changes in the aging neurogenic niche. This study should provide unique mechanistic insights into the regulation of transcriptional outputs, including transcriptional noise versus consistency, and how they are altered during aging in regenerative cells. This study should also provide a fundamental understanding of aging in a complex system, comprising a population of regenerative and more committed cells. Together, this knowledge should pave the way for building new methods for `epigenetic reprogramming' of old cells to restore youthful function to old cells and tissues.